CONSTANT SURFACE TEMP VS CONSTANT HEAT FLUX
CONSTANT SURFACE TEMP VS CONSTANT HEAT FLUX
(OP)
I HAVE A HARD TIME UNDERSTANDING THE APPLICATION OF CONSTANT SURFACE TEMPERATURE AND CONSTANT HEAT FLUX. AND WAS HOPING SOMEONE CAN DUMB IT DOWN FOR ME.
FOR AIR COOLED HEAT EXCHANGERS THE INTERNAL HEAT TRANSFER COEFFICIENT'S NUSSELT NUMBER VALUE FOR THE LAMINAR REGIME DEPENDS ON BEING EITHER SUBJECTED TO CONSTANT SURFACE TEMPERATURE OR CONSTANT HEAT FLUX. I AM CONFUSED IN WHICH IS USED FOR AIR COOLED HEAT EXCHANGERS.
THANK YOU FOR YOUR HELP.
FOR AIR COOLED HEAT EXCHANGERS THE INTERNAL HEAT TRANSFER COEFFICIENT'S NUSSELT NUMBER VALUE FOR THE LAMINAR REGIME DEPENDS ON BEING EITHER SUBJECTED TO CONSTANT SURFACE TEMPERATURE OR CONSTANT HEAT FLUX. I AM CONFUSED IN WHICH IS USED FOR AIR COOLED HEAT EXCHANGERS.
THANK YOU FOR YOUR HELP.





RE: CONSTANT SURFACE TEMP VS CONSTANT HEAT FLUX
What is your exact application?
RE: CONSTANT SURFACE TEMP VS CONSTANT HEAT FLUX
As I said it is for an air cooled heat exchanger, hot fluid is going through the tubes and cool ambient air is blown over it to cool the hot fluid.
RE: CONSTANT SURFACE TEMP VS CONSTANT HEAT FLUX
RE: CONSTANT SURFACE TEMP VS CONSTANT HEAT FLUX
A "bulk" temperature is assumed for any position along the heat tansfer surface to represent the total energy of flow at a location along the tube. Heat transfer coefficient is a function of the wall temperature and the bulk temperature. Nusselt will be constant (Nu=hd/k).
RE: CONSTANT SURFACE TEMP VS CONSTANT HEAT FLUX
In a constant heat flux condition, the convective heat loss is either all of, or the bulk of, the heater heat load, i.e., the heat flux has already done its intended purpose and is now completely waste heat.
TTFN
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RE: CONSTANT SURFACE TEMP VS CONSTANT HEAT FLUX
As an aside, some electrically heated exchangers maintain process temperatures at constant heat fluxes notwithstanding the degree of fouling. Of course, the temperature on the surface of heating element goes up until a allowable limit is reached and shutdown for cleaning is called for.